In a conventional inflatable restraint system, a sensor is used to detect the occurrence of a vehicle impact and, upon such occurrence, to deploy an inflatable cushion. Once deployed with inflation gas, the inflatable cushion provides a layer between the passenger of a vehicle and the hard surfaces of an automotive interior during vehicle impact. These systems are highly effective and have saved lives in thousands of vehicles. For some passenger and impact situations, however, the conventional inflatable restraint systems are not optimized. These situations may occur, for example, with passengers who are much smaller than the average adult, with passengers who are unbelted or "out-of-position," or in low severity impacts. In such cases, conventional inflatable restraint system may deploy an inflatable cushion with less-than-optimal energy absorption characteristics, such as excessive force.
Various techniques have been explored to control the energy absorption characteristics of the inflatable cushion. One such technique uses a dual level inflator. In these systems, a first inflator charge is used to deploy the inflatable cushion with inflation gas upon the detection of a vehicle impact, and the second inflator charge is used to further inflate the inflatable cushion only in response to specific situations. These techniques, however, suffer from the expense and complication of using such a dual level inflator.
Another such technique, as described in U.S. Pat. No. 5,074,583 (Fujita et al.), uses a discharge valve to allow ventilation of the inflatable cushion when the pressure in the inflatable cushion reaches a certain level. The ventilation of the inflatable cushion through the discharge valve limits and reduces the pressure in the inflatable cushion and may prevent the deployment of an inflatable cushion with excessive force. This technique, however, only allows control of the pressure of the inflatable cushion and does not allow any control of the energy absorption characteristic of the inflatable cushion in response to different passenger and impact situations.
Other, more recent, techniques use movable shutters, instead of discharge valves, that may be selectively activated. The ventilation of the inflatable cushion through the movable shutters also alters the energy absorption characteristics of the inflatable cushion by reducing the pressure in the inflatable cushion. Unlike the discharge valve technique, the movable shutters allows control of the energy characteristics of the inflatable cushion in response to different passenger situations. But, because of the slow response of the mechanical shutters, these techniques do not allow control of the energy absorption characteristics of the inflatable cushion in response to low severity impacts. Vehicle impacts occur too fast for a determination of a low severity impact and for an appropriate mechanical response.
Thus, the current techniques in the art fail to provide a simple, cost-effective technique to control the energy absorption characteristics of the inflatable cushion in response to passengers who are much smaller than the average adult, passengers who are unbelted or "out-of-position," and low severity impacts.